1. Field of the Invention
This invention relates to improvements in techniques for the formation of felts, and in particular thick felts such as those used for heat and sound insulation.
2. Background of the Prior Art
The formation of felts from fibers carried by a gaseous current is traditionally carried out by passing this current through a perforated receiving conveyor which holds back the fibers. To bond the fibers to each other, a binder is sprayed over the fibers in the course of their path to the receiving conveyor. This binder is subsequently hardened, for example by a heat treatment.
This technique is employed in particular for the production of mineral fiber felts. Hereinafter the formation of felts from fibers of vitreous materials is exclusively referred to due to the importance of this type of production but the invention is nevertheless applicable to all processes of producing felts, whether from mineral or from organic fibers.
One of the difficulties encountered in the preparation of these felts is connected with the uniform distribution of the fibers within the felt. The gaseous current carrying the fibers normally has a cross section of limited width which is a function, in particular, of the apparatus used for the production of the fibers. Moreover, the gaseous current normally does not cover the whole width of the conveyor, and the fibers are not uniformly distributed.
Various means have been proposed for improving the distribution of the fibers on the conveyor. One of the most useful of these means is of the type described in U.S. Pat. No. 3,134,145. It consists of passing the gaseous flux carrying the fibers through a guide duct. This duct is movable and is subjected to an oscillating movement which alternately directs the gaseous flux from one edge to the other of the conveyor receiving the fibers.
If the operating conditions are suitably chosen, the fibers are deposited by these means over the whole width of the conveyor.
In practice, however, it has been found that a strictly uniform distribution is very difficult to obtain. Deviations of the mass of fibers per unit surface area of as much as 15% or more from the mean value are encountered in samples taken at different points over the width of the felt. It is therefore necessary to improve the practical execution of this technique of distribution in order to reduce as much as possible the variations found in the distribution of the fibers.
It is an object of this invention to provide an improved technique for the distribution of fibers in the formed felts.
The invention particularly has the object of providing a process whereby variations in distribution appearing in the course of operation can be corrected.
The invention also has the aim of enabling the correction in the variations of fiber distribution to be carried out automatically.